﻿using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
public partial class YqhCheckCode : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //创建验证码对象
        ValidateCode obj = new ValidateCode();

        Session["yzm"] = obj.RandomNum(4);

        obj.CreateImages(Session["yzm"].ToString());
    }

    /// <summary>
    /// 验证码
    /// </summary>
    public class ValidateCode
    {
        /// <summary>
        /// 验证码构造函数
        /// </summary>
        public ValidateCode()
        {
        }

        /// <summary>
        /// 生成验证图片
        /// </summary>
        /// <param name="ValidateCode">验证字符</param>
        public void CreateImages(string ValidateCode)
        {
            int iwidth = (int)(ValidateCode.Length * 13);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 23);
            Graphics g = Graphics.FromImage(image);
            g.Clear(Color.White);
            //定义颜色
            Color[] c = {
                        Color.Black,
                        Color.Red,
                        Color.DarkBlue,
                        Color.Green,
                        Color.Orange,
                        Color.Brown,
                        Color.DarkCyan
                        ,Color.Purple
                    };
            //定义字体
            string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };
            Random rand = new Random();
            //随机输出背景
            for (int i = 0; i < 50; i++)
            {
                int x = rand.Next(image.Width);
                int y = rand.Next(image.Height);
                g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);
            }

            //输出不同字体和颜色的验证码字符
            for (int i = 0; i < ValidateCode.Length; i++)
            {
                int cindex = rand.Next(7);
                int findex = rand.Next(5);

                Font f = new System.Drawing.Font(font[findex], 10, System.Drawing.FontStyle.Bold);
                Brush b = new System.Drawing.SolidBrush(c[cindex]);
                int j = 4;
                if ((i + 1) % 2 == 0)
                {
                    j = 2;
                }
                g.DrawString(ValidateCode.Substring(i, 1), f, b, 3 + (i * 12), j);
            }
            //画一个边框
            g.DrawRectangle(new Pen(Color.Black, 0), 0, 0, image.Width - 1, image.Height - 1);

            //输出到浏览器
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.ContentType = "image/Jpeg";
            HttpContext.Current.Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            image.Dispose();
        }

        /// <summary>
        /// 生成随机数
        /// </summary>
        /// <param name="codeNum">生成字母的个数</param>
        /// <returns>string</returns>
        public string RandomNum(int codeNum)
        {
            char[] arrChar = new char[] { 'a', 'b', 'd', 'c', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'p', 'r', 'q', 's', 't', 'u', 'v', 'w', 'z', 'y', 'x', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'Q', 'P', 'R', 'T', 'S', 'V', 'U', 'W', 'X', 'Y', 'Z' };
            System.Text.StringBuilder strOut = new System.Text.StringBuilder();
            //记录上次随机数值，尽量避免生产几个一样的随机数
            int temp = -1;

            //采用一个简单的算法以保证生成随机数的不同
            Random rand = new Random();
            for (int i = 1; i < codeNum + 1; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(arrChar.Length);
                if (temp != -1 && temp == t)
                {
                    return RandomNum(codeNum);
                }
                temp = t;
                strOut.Append(arrChar[t].ToString());
            }
            return strOut.ToString();
        }
    }
}
